Changes in Matter

Chapter Sixteen: Acids, Basesand Solutions

• 16.1 Water and Solutions

• 16.2 Acids, Bases, and pH

Investigation 16A

• What does it mean to dissolve?

Solubility

16.1 Water and solutions

• A solution is a mixture of two or more substances that is uniform at the molecular level.

16.1 Water and solutions

• Although we often think of solutions as mixtures of solids in liquids, solutions exist in every phase; solid, liquid, or gas.

• Solutions of two or more solids are called alloys.

• Steel is an alloy (solution) of iron and carbon.

16.1 Water and solutions

• A solution contains at least two components: a solvent, and a solute.

• The solvent is the part of a mixture that is present in the greatest amount.

Which of these is the solvent?

16.1 Water and solutions

• When the solute particles are evenly distributed throughout the solvent, we say that the solute has dissolved.

16.1 Solubility

• The term solubility means the amount of solute (if any) that can be dissolved in a volume of solvent.

Is there a limit for how much seltzer (solute) can dissolve in water (solvent)?

16.1 Solubility• Chalk and talc do

not have solubility values.

• These substances are insoluble in water because they do not dissolve in water.

16.1 Solubility

• A solution is saturated if it contains as much solute as the solvent can dissolve.

• Any solute added in excess of the substance’s solubility will not dissolve.

What will happen to any un-dissolved gas when you unscrew the cap of seltzer water?

16.1 Concentration

• In chemistry, it is important to know the exact concentration of a solution—that is the exact amount of solute dissolved in a given amount of solvent.

16.1 Concentration• When a solute like sugar is mixed with a

solvent like water, two processes are actually going on continuously.– Molecules of solute dissolve and go into

solution.– Molecules of solute come out of solution

and become “un-dissolved.”

• When the rate of dissolving equals the rate of coming out of solution, we say equilibrium has been reached.

16.1 Water and solutions

• A supersaturated solution means there is more dissolved solute than the maximum solubility.

16.1 Solubility of gases in liquids

• When you drink carbonated soda, the fizz comes from dissolved carbon dioxide gas (CO2).

• The solubility of gases in liquids increases with pressure.

16.1 Solubility of gases in liquids

• Oil and vinegar salad dressing separates because oil is not soluble in water.

• Liquids that are not soluble in water may be soluble in other solvents.

16.1 Water as a solvent

• Water is often called the “universal solvent.”

• Water is a good solvent because of the way the H2O molecule is shaped.

16.1 Water as a solvent

• A water molecule has a negative end (pole) and a positive end.

• A molecule (like water) with a charge separation is called a polar molecule.

16.1 Water as a solvent

• Water dissolves sodium chloride (salt) to form a solution of sodium (+) and chlorine (-) ions.

16.1 Water as a solvent

• In general, like dissolves like: – water dissolves

polar substances– non-polar solvents

dissolve non-polar substances